Benjamin J. Powers, MD, MHS; Maren K. Olsen, PhD; Valerie A. Smith, MS; Robert F. Woolson, PhD; Hayden B. Bosworth, PhD; Eugene Z. Oddone, MD, MHSc
The optimal setting and number of blood pressure (BP) measurements that should be used for clinical decision making and quality reporting are uncertain.
To compare strategies for home or clinic BP measurement and their effect on classifying patients as having BP that was in or out of control.
Secondary analysis of a randomized, controlled trial of strategies to improve hypertension management. (ClinicalTrials.gov registration number: NCT00237692)
Primary care clinics affiliated with the Durham Veterans Affairs Medical Center.
444 veterans with hypertension followed for 18 months.
Blood pressure was measured repeatedly by using 3 methods: standardized research BP measurements at 6-month intervals; clinic BP measurements obtained during outpatient visits; and home BP measurements using a monitor that transmitted measurements electronically.
Patients provided 111 181 systolic BP (SBP) measurements (3218 research, 7121 clinic, and 100 842 home measurements) over 18 months. Systolic BP control rates at baseline (mean SBP <140 mm Hg for clinic or research measurement; <135 mm Hg for home measurement) varied substantially, with 28% classified as in control by clinic measurement, 47% by home measurement, and 68% by research measurement. Short-term variability was large and similar across all 3 methods of measurement, with a mean within-patient coefficient of variation of 10% (range, 1% to 24%). Patients could not be classified as having BP that was in or out of control with 80% certainty on the basis of a single clinic SBP measurement from 120 mm Hg to 157 mm Hg. The effect of within-patient variability could be greatly reduced by averaging several measurements, with most benefit accrued at 5 to 6 measurements.
The sample was mostly men with a long-standing history of hypertension and was selected on the basis of previous poor BP control.
Physicians who want to have 80% or more certainty that they are correctly classifying patients' BP control should use the average of several measurements. Hypertension quality metrics based on a single clinic measurement potentially misclassify a large proportion of patients.
U.S. Department of Veterans Affairs Health Services Research and Development Service.
Blood pressure readings obtained during clinical encounters are generally used to determine the adequacy of treatment of hypertension and are increasingly used as measures of quality of care.
In a secondary analysis of a large, randomized, clinical trial, blood pressure varied widely in the short term, whether measured in the home, clinic, or research setting. A single measurement was generally inadequate to correctly determine whether blood pressure was being adequately controlled.
Most patients were men with previous poor control of blood pressure.
Several measurements are needed to assess blood pressure control. A single blood pressure recording is not a meaningful quality metric.
SBP = systolic blood pressure. A. Patient with high within-patient variability. Mean clinic measurement was 135 mm Hg (SD, 17); coefficient of variation = 0.128. Mean home measurement was 118 mm Hg (SD, 15); coefficient of variation = 0.125. B. Patient with low within-patient variability and high correlation among home, clinic, and research measurements. Mean clinic measurement was 139 mm Hg (SD, 8); coefficient of variation = 0.054. Mean home measurement was 131 mm Hg (SD, 10); coefficient of variation = 0.073. C. Patient with consistently higher clinic SBP compared with home measurement (i.e., white-coat hypertension). Mean clinic measurement was 135 mm Hg (SD, 18); coefficient of variation = 0.133. Mean home measurement was 124 mm Hg (SD, 9); coefficient of variation = 0.074. D. Patient with consistently higher home SBP than clinic or research SBP (i.e., masked hypertension). Mean clinic measurement was 130 mm Hg (SD, 21); coefficient of variation = 0.160. Mean home measurement was 139 mm Hg (SD, 19); coefficient of variation = 0.139.
Results are from a group of mostly male patients who received treatment for hypertension and had a history of elevated blood pressure measurements. Results may differ in other samples. The total individual variance combines both the between- and the within-patient variance and is calculated as the variance is reduced by taking the mean of increasing number of measurements. Random-effects models were used to derive estimates of the within-patient variance for each mode of assessment. Research variance is calculated from a model using all 18 months of data, whereas clinic and home variances are based on the average of multiple, shorter time frames. Details of the derivations are provided in the Appendix. SBP = systolic blood pressure.
Results are from a group of mostly male patients who received treatment for hypertension and had a history of elevated blood pressure measurements. Results may differ in other samples. SBP = systolic blood pressure. Left. Clinic measurement. Right. Home measurement.
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The Ohio State University
June 23, 2011
Use of Quality Metrics Must Reflect the Literature
The research by Powers et al in the June 21 issue of Annals is not only important clinically, but it also has direct relevance to the ongoing evolution in the health care system (1). Hypertension is the most common cardiovascular disease in the United States and is often the initial insult on the road to coronary artery disease and heart failure (2). As such, it is not surprising that blood pressure level is a common quality parameter used by the National Committee for Quality Assurance (NCQA), the Centers for Medicare and Medicaid Services, and various insurers (3).
As the country moves to public reporting for outcomes, and physicians and systems begin organizing into Accountable Care Organizations with a focus on quality, it is important that quality indicators such as blood pressure level be based on the science. In the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, findings demonstrated that the current target blood pressure of less than 130/80 mmHg was inappropriate in many diabetic patients and actually lead to increased cardiac events (4). Despite this, a blood pressure goal of < 130/80 mmHg is the metric used by the NCQA and others as a marker of "quality". This "quality" metric is based on a single reported blood pressure. In their work, Powers et al conclude that "Quality metrics based on a single clinical measurement potentially misclassify a large portion of patients" (1).
It is imperative that stakeholders and policymakers acknowledge that quality in medicine does not always lend itself to a hard number that can be applied to all patients. Should such entities continue to do so, patient outcomes will suffer, and physician's actions will be based on treating a number, not treating the patient.
1. Powers BJ, Olsen MK, Smith VA, et al. Measuring blood pressure for decision making and quality reporting: where and how many measures. Ann Intern Med. 2011;154:781-877
2. Roberts CK, Barnard J. Effects of exercise and diet on chronic disease. J Appl Physiol. 205;98:3-30.
3. http://www.ncqa.org/tabid/139/Default.aspx. Accessed 6-23-11
4. Cushman WC, Evans GW, Byington RP, et al. Effects of intensive blood- pressure control in type 2 diabetes mellitus. N Engl J Med. 2010;362:1575- 85
Omega C. Logan Silva
George Washington University, Past President, American Medical Women's Association
June 28, 2011
Why not discuss the way to take a blood pressure?
I read with great interest the article on Measuring Blood Pressure for Decision Making and Quality Reporting: Where and How Many Measures and I agreed with most of the article, but I wondered why the authors did not discuss the proper way to physically take a blood pressure? Maybe what I was taught is out of date, but is not the position of the arm, the level of the arm in relation to the heart, and the size of the cuff important to obtaining an accurate reading?
Uday A Gupta
Department of Cardiorespiratory physiology, Vallabhbhai Patel Chest Institute, Unversity of Delhi, D
July 25, 2011
Accuracy, acceptability, repeatability and reproducibility in blood pressure measurement
When biological signals are recorded, following issues are relevant - 'accuracy', 'acceptability', 'repeatability' and 'reproducibility' [1,2].
'Accuracy' is closeness of agreement between the measurement and the conventional true value [1,2]. This depends on limitations of principles of the measurement technique and also the equipment design and built.
'Acceptability' refers to whether the particular single recording has been done with the recommended method. Each and every recording of biological signals has to be 'acceptable'.
'Repeatability' is the closeness of agreement between the results of successive measurements of the same item carried out, subject to all of the following same conditions: same method, same observer, same instrument, same location, same condition of use, and repeated over a short space of time [1,2]. There is no data, to the best of my knowledge that quantifies variation in repeatability in BP measurement at the point of care and then applies evidence based, validated criteria to account for variation due to repeatability considerations.
'Reproducibility' is the closeness of agreement of the results of successive measurements of the same item where the individual measurements are carried out with changed aforesaid conditions. White coat hypertension is an example of variation due to reproducibility considerations. The variation measured by the present  and many past studies are descriptions of reproducibility, not repeatability. The data have been recorded and analyzed together for different locations, observers, conditions of use and time. These analyses of reproducibility are of course welcome and necessary.
Guidelines on BP recording do not clearly differentiate between repeatability and reproducibility. The American Heart Association statement  says that 2-3 readings in morning and evening each be clubbed with recordings over a week for interpretation. The European Society of Hypertension  recommends at least two measurements at 1 min intervals and then gives subjective criteria for repeat measurements. The AHA statement writes that blood pressure can vary by up to 20 mmHg between recordings in home. How much of this variation is due to repeatability considerations and how much is due to reproducibility considerations?
There is a need that for the commonly used methods of BP measurement, criteria for 'accuracy', 'acceptability', 'repeatability' and 'reproducibility' be available like they are for spirometry [1,2]. These criteria will have to be a balance between what is clinically relevant and what is practically feasible. The target is to make BP recordings that are accurate, acceptable, repeatable and reproducible.
1. ATS/ERS task force: standardisation of lung function testing. General considerations for lung function testing. Eur Respir J. 2005; 26: 153-161.
2. International vocabulary of basic and general terms in metrology. PD 6461 Vocabulary of Metrology. Part 1: Basic and general terms (international). 2nd Edn. Geneva, International Standards Organisation, 1993.
3. Powers BJ, Olsen MK, Smith VA, et al. Measuring blood pressure for decision making and quality reporting: where and how many measures? Ann Intern Med. 2011;154:781-788.
4. Pickering TG, Miller NH, Ogedegbe G, et al. Call to action on use and reimbursement for home blood pressure monitoring: Executive Summary. A joint scientific statement from the American Heart Association, American Society of Hypertension, and Preventive Cardiovascular Nurses Association. J Clin Hypertens (Greenwich). 2008;10:467-76.
5. O'Brien E, Asmar R, Beilin L, et al. European Society of Hypertension recommendations for conventional, ambulatory and home blood pressure measurement. J Hypertension 2003, 21:821-848.
Benjamin J. Powers
Duke University and Durham VAMC
August 2, 2011
Author Response to Reader Comments
As Dr. Silva points out, the common errors of a poorly fitting cuff, instrument mis-calibration or sloppy technique all contribute to imprecise blood pressure measurement. Unless we insist on high standards for BP measurement, the reported value may not hold much meaning.(1) In addition there are common biases from terminal digit preference (i.e. the tendency to report manual readings with a 0 or a 5) and re-measurement of blood pressure only when the initial value is high, but never when it is normal. There is substantial room for improvement in our implementation of standards for blood pressure measurement.
However, we believe our data also suggest that focusing only on the technical aspects of clinic measurement misses the point that no matter how carefully blood pressure is measured, it can vary substantially from hour to hour or day to day. Over our 18month study, the coefficient of variation was nearly identical for BP measured in the clinic, research setting, or at home. This argues against technique as the primary source of variation. Home blood pressure measurement eliminates white-coat effects, is a much stronger predictor of vascular risk than clinic readings, (2, 3) and more practically - it allows decision making based on multiple measurements. So while we can significantly improve how blood pressure is measured, we believe it is even more important that future guidelines emphasize where it is measured and how that information should be used for clinical decision making. Current evidence suggests that decisions made based on home blood pressure result in the use of fewer medications and lower overall treatment costs without an apparent increase in end-organ damage.(4)
We agree with the comment by Dr. Wexler about the importance of quality metrics actually reflecting high quality decision making. While these metrics were created primarily to evaluate the practice of medicine, it is clear that they also influence it. When hypertension quality metrics promote treatment decisions based on a single clinic reading, they risk more than just inaccurate assessment of quality, but also patient harm. For patients with hypertension under the care of a physician, future guidelines should include recommendations for where BP should be measured, and how many measurements should be averaged to guide treatment decisions.
1. Ogedegbe G, Pickering T. Principles and techniques of blood pressure measurement. Cardiol Clin. 2010;28(4):571-86.
2. Bobrie G, Chatellier G, Genes N, Clerson P, Vaur L, Vaisse B, et al. Cardiovascular Prognosis of "Masked Hypertension" Detected by Blood Pressure Self-measurement in Elderly Treated Hypertensive Patients. JAMA. 2004;291(11):1342-9.
3. Niiranen TJ, Hanninen MR, Johansson J, Reunanen A, Jula AM. Home- measured blood pressure is a stronger predictor of cardiovascular risk than office blood pressure: the Finn-Home study. Hypertension. 2010;55(6):1346-51.
4. Verberk WJ, Kroon AA, Lenders JW, Kessels AG, van Montfrans GA, Smit AJ, et al. Self-measurement of blood pressure at home reduces the need for antihypertensive drugs: a randomized, controlled trial. Hypertension. 2007;50(6):1019-25.
Benjamin J. Powers, Maren K. Olsen, Valerie A. Smith, Robert F. Woolson, Hayden B. Bosworth, Eugene Z. Oddone. Measuring Blood Pressure for Decision Making and Quality Reporting: Where and How Many Measures?. Ann Intern Med. 2011;154:781–788. doi: 10.7326/0003-4819-154-12-201106210-00005
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Published: Ann Intern Med. 2011;154(12):781-788.
Cardiology, Coronary Risk Factors, Hypertension, Nephrology.
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